A wire is made up of a $3.0\,\text{m}$ section of metal X joined to a $1.0\,\text{m}$ section of metal Y. The wire has a constant cross-sectional area throughout. When a load is suspended from the wire, metal X increases in length by $1.5\,\text{mm}$ and metal Y increases in length by $1.0\,\text{mm}$. The same load is then suspended from a second wire with the same cross-sectional area, but this time it contains a $1.0\,\text{m}$ section of metal X and a $3.0\,\text{m}$ section of metal Y. For both wires, the extension stays within the limit of proportionality. What is the total extension of this second wire?
- A$2.5\,\text{mm}$
- B$3.5\,\text{mm}$
- C$4.8\,\text{mm}$
- D$5.0\,\text{mm}$